This should be animating:

The program for this is:

>     #lang whalesong

>     (require whalesong/resource
>              whalesong/web-world)

>     (define-resource index.html)
>     (define-resource style.css)

>     (define (tick w v)
>       (modulo (add1 w) 10))

>     ;; pick-block: world view -> view
>     ;; Focus the view on block i.
>     (define (pick-block v i)
>       (view-focus v (format "~a" i)))

>     (define (draw w v)
>       (define v1 (update-view-attr
>                   (pick-block v w)
>                   "class"
>                   "selectedBlock"))
>       (define v2 (update-view-attr
>                   (pick-block v1 (modulo (sub1 w) 10))
>                   "class"
>                   "offsetBlock"))
>       (define v3 (update-view-attr
>                   (pick-block v2 (modulo (add1 w) 10))
>                   "class"
>                   "offsetBlock"))
>       (define v4 (update-view-attr
>                   (pick-block v3 (modulo (- w 2) 10))
>                               "class"
>                               "block"))
>       (define v5 (update-view-attr
>                   (pick-block v4 (modulo (+ w 2) 10))
>                   "class"
>                   "block"))
>       v5)

>     (big-bang 0
>               (initial-view index.html)
>               (on-tick tick)
>               (to-draw draw))

with `style.css`:

>     .block {
>         width : 80px;
>         height : 10px;
>         background-color : blue;
>         display: inline-block;
>     }

>     .selectedBlock {
>         width : 80px;
>         height : 10px;
>         background-color: navy;
>         display: inline-block;
>     }

>     .offsetBlock {
>         width : 80px;
>         height : 10px;
>         background-color: teal;
>         display: inline-block;
>     }